It is claimed by the inventor (Dr. Ramesh Chandra Gupta, Ph. D., P.E.) that with the use of the expandable jacket around the soil specimen, a uniform increase in diameter of the cylindrical specimen of soils and intermediate geomaterials shall occur through its height without any localized bulging or formation of a barrel shape, permitting accurate calculation of new area of cross-section at any instant of time, when axial vertical load is applied during the triaxial compression test. New area of cross-section is required to calculate the deviator stress during the process of shearing at any instant of time. So far for more than 100 years, the criticism of triaxial test has been that during the test, barrel shape sometimes with localized bulging forms, resulting in premature failure of the specimen, inaccurate determination of the area of cross-section, the deviator stress, and affecting the accuracy of volume change characteristics.
The expandable jacket consists of the rubber membrane surrounding the cylindrical specimen, circular segmental metal plates surrounding the rubber membrane, and elastomeric rubber bands or rings around the segmental plates to permit uniform radial expansion and maintain uniform diameter of the specimen during the test and thereby providing accurate values of deviator stress, volume change characteristics and shear strength of soils and intermediate geomaterials. For the above purpose, the expandable jacket surrounding the cylindrical specimen of soils and intermediate geomaterials shall be used during triaxial compression tests. For the same purpose, to determine accurate value of the unconfined compressive strength without permitting the barrel shape to form, the expandable jacket surrounding the cylindrical specimen of the cohesive soils, soft and jointed or fissured rocks shall be used during the unconfined compression tests.
So far, because barrel shape always formed during these compression tests on soils and intermediate geomaterials, LVDT measurement of the radial expansion of the specimen was not being done, but now with invention of expandable jacket and flexible ring, the measurement of radial expansion by LVDT becomes an attractive item during the test. During triaxial compression, unconfined compression and uniaxial compressive strength tests, both vertical displacement and radial displacement/expansion occurs simultaneously and when LVDT is placed in contact with the surface of the cylindrical specimen for measuring the radial expansion of the specimen, LVDT probe in contact with the specimen gets bent or inclined due to the vertical displacement of the specimen, resulting in inaccurate readings and many times damaging the probe. To prevent this to happen, a spring-loaded U-frame resting on ball bearings has been invented to mount the LVDT probe in it. The U-frame can move horizontally with LVDT probe affording the measurement of radial expansion, while specimen vertically compress along lubricated face of the U-frame. The measurement of radial expansion by LVDT mounted in the U-frame shall permit determination of accurate values of Poisson's ratio. When, LVDT measurements are done in a pressure chamber or sealed reservoir, it is necessary to select a suitable LVDT which can withstand the fluid pressures without damage to the electronics in it and then it is necessary to provide a sealed exit for the cable of LVDT without creating leakage in the pressure chamber. Even in open reservoir a right selection of LVDT is required. A proper design for the sealed exit have to be made as provided in this application.
For more than 100 years, the coefficient of consolidation and dissipation of excess pore-water pressures have been determined only in vertical direction using one-dimensional consolidation tests. However, in the field, this very seldom or never happens, because settlement, consolidation and dissipation of excess pore-water pressures always occurs both in horizontal and vertical directions. To simulate true field behavior, three-dimensional consolidation test has been invented using a flexible ring which is like the expandable ring as far as most structural components are concerned, except that a filter fabric or paper is wrapped around the cylindrical specimen, and then rubber membrane is mounted surrounding the filter paper or paper. The presence of the fabric filter or filter paper surrounding the cylindrical specimen of soils and intermediate geomaterials shall allow dissipation of excess pore-pressures in horizontal direction and porous discs above and below the cylindrical specimen shall allow dissipation of excess pore-pressures in vertical direction; and the flexible ring shall permit uniform radial expansion of the specimen simultaneously with vertical displacement under vertical load, thus simulating field conditions.
For saturated soils, excess pore-water expelled out of the specimen during the test can be collected in burette of the control panel and help in determination of radial expansion and thereby calculation of Poisson's ratio for both during triaxial tests and three-dimensional consolidation tests, but for partially saturated soils, the radial expansion can be approximately calculated by using assumed values of Poisson' ratio as available in literature. For calculating accurate values of the radial expansion of the cylindrical specimen of the partially saturated soils and intermediate geomaterials and Poisson's ratio, measurement of the radial expansion by LVDT mounted in spring-loaded U-frame moving on ball bearings as invented with this application, is required to be done.
For calibration of expandable jacket and flexible ring and to determine modulus of elasticity of rubber membrane and combined modulus of elasticity of expandable jacket and flexible ring, a calibration device has been invented, which consist of a vertically movable water reservoir, a horizontal porous metal tube connected to movable water reservoir, via at least one tube, wherein porous metal tube is configured to be surrounded and sealed by an additional rubber membrane and wherein the additional rubber membrane is configured to be surrounded by a combination of the filter fabric or filter paper, the rubber membrane, the segmental metal plates, and the at least one elastomeric rubber band.